I think the OP needs to go back to the basics first.. Good bedding, and good form.. Check the bedding, Check the barrel relief. Check the screw tension. Then do a work up of his loads.. And as he stated if one brand and weight of bullet causes a problem then try something else. As you know working up a good load for a particular rifle can take time, and patience.
I also know that if you are not doing a good repeatable rest technique it can cause horizontal stringing.. I have also seen cracked bedding cause problems.. Loose scope mounts. Or any number of mechanical things..
Now I would ask the OP how the other loads printed? And what results has he seen using other brands of bullets? But I think he stated that only thios one bullet was stringing.. If he still has some bullets left test em again against a known good load.
